Ventricular fibrillation is the most common etiology leading to sudden cardiac death. Early defibrillation and non-interrupted Cardio Pulmonary Resuscitation are the most important determinants for restoration of spontaneous circulation in patients with VF. The occurrence of VF out of hospital makes early defibrillation hard to be realized. Fortunately, the VF waveform analysis such as amplitude spectrum analysis (AMSA) could help estimate the duration of VF, determine the shock ability by assessing the VF waveform as being fine or coarse, and predict the probability of successful defibrillation, and has been applied to the conventional Automatic External Defibrillator (AED) for providing early defibrillation during the occurrence of VF out of hospital.
Although studies have demonstrated interruption of CPR greatly decreases the probability of successful resuscitation, non-interrupted CPR during recording Electrocardiography (ECG) for the VF waveform analysis is still a challenge. Empirical mode decomposition (EMD) is a signal analysis method which has received much attention lately due to its application in a number of fields. The problem of mode mixing in Empirical Mode Decomposition is caused by the intermittency signals and noises, which is defined as a single Intrinsic Mode Function (IMF) consisting of signals of widely disparate scales. The mode mixing of EMD is caused by the input data consisting of intermittent oscillations of two or multi scales, a low frequency component and another higher frequency component occurring only at some part of the signal. In this situation, the sifting process detects the extrema of higher frequency component in some parts of the signal and detects the extrema of low frequency component for other parts of the signal. Then the locations of extrema are highly non-uniformly distributed and the extrema detected in the sifting process belong to different signals, therefore the decomposed IMF will contain mixed modes.
Suppose a signal consists of many tones with frequencies. A tone is distributed into many IMFs after the decomposition. The IMF contains the most energy of tone is designated as the major component of the tone and other IMFs are designated as the minor component of the tone. Then the mode splitting effect is defined as the leakage of the tone into other IMFs with indices.
The mode splitting effect is a natural consequence of EMD and its degree can be measured. The frequency ratio of the low frequency to higher frequency component or extrema (distribution) rate ratio is the source for producing mode splitting. As the extrema rate ratio is closer to one, then the mode splitting become more severe.